Runkun Zhao

Ultrafast, high-precision roll-angle metrology is crucial for dynamic motion control yet remains challenging because roll is not directly accessible to conventional geometric optical methods. Here, we present a roll-angle measurement method based on a polarization-modulated optical frequency comb (PMOFC). By modulating the offset frequency, a sequence of femtosecond pulses with periodically varying polarization was generated. After passing through a birefringent target and a fixed-angle analyzer, the roll angle is retrieved from the corresponding intensity sequence. Experimental results demonstrate an absolute non-ambiguous range of 0°–90°, and a single-shot measurement time of ∼71 ns. At the worst-case angular position, the Allan deviation decreases below 20 ^{′ ′} after 3.93 μs of averaging. These results establish a practical route to high-rate absolute roll-angle measurement.

High-precision six-degree-of-freedom (6-DOF, pitch, yaw, roll, axial displacement, and two lateral displacements) measurement is essential in advanced manufacturing and precision assembly, particularly in aerospace, semiconductors, and precision engineering. However, achieving high-precision absolute 6-DOF measurement directly on the target remains challenging. This study proposes a novel method for absolute 6-DOF measurement directly on non-cooperative targets, employing low-coherence light and temporal phase-shifting. This method extracts position and orientation information from the coherence envelope shape and the geometric texture of the target background without relying on cooperative targets. The proposed method achieves favorable results in verifying the resolution, linearity, and repeatability indicators of 6-DOF. Additionally, a simulation of the 6-DOF tracking of a satellite antenna central support plate during the manufacturing process demonstrates good agreement between the measured and reference values. This study presents a novel approach for high-precision absolute and direct 6-DOF measurements on non-cooperative targets, offering significant guidance for the processing and assembly of aerospace components in advanced manufacturing.

Dual-comb ranging is a typical absolute-distance measurement method. Noise in ranging systems limits improvements in ranging precision. Timing jitter is a primary noise source, and its relationship with ranging precision remains to be explored. In this study, we established a model to describe this relationship from the perspective of the noise power spectral density (PSD). We propose a corresponding simulation method and analyze the coupling between the timing jitter and intensity noise. Furthermore, we validated this model using dual combs with different noise levels, including the measurement of timing jitter PSD and analysis of ranging precision, which confirms the correctness of our model. The proposed model for timing jitter and ranging precision can help comprehend the mechanism and design dual-comb ranging systems for practical applications.